The studies proposed in this application are directed toward defining the primary structural diversity among antibodies that are specific for the same antigen and determining the genetic mechanisms that generate the diversity. These issues will be addressed through electrophoretic, idiotypic, and amino acid sequence analyses of anti-streptococcal group A carbohydrate antibodies elicited in strain A mice at three levels of immunocompetence: (1) Early in ontologic development (neonates), (2) Primary immunized (single antigenic stimulus) adults, and (3) Secondary immunized repeated antigenic stimuli) adults. The substrates for these studies are hybridoma antibody products obtained by in vitro cell-fusion of immune spleen cells and antigen-simulated spleen fragments with plasmacytoma cells. These analyses will reveal the relative contribution to the functional antibody repertoire of germ-line encoded variability versus somatically acquired variability, and the respective roles of somatic development and antigenic stimulation in generating antibody diversity.